I. Field
The present invention relates generally to communications and more specifically to data transmission in a wireless multiple-access communication system.
II. Background
A wireless multiple-access system can concurrently support communication for multiple wireless terminals on the forward and reverse links. The forward link (or downlink) refers to the communication link from base stations to terminals, and the reverse link (or uplink) refers to the communication link from terminals to base stations. Multiple terminals may simultaneously transmit data on the reverse link and/or receive data on the forward link. This may be achieved by multiplexing the data transmissions on each link to be orthogonal to one another in time, frequency, and/or code domain. The orthogonality ensures that the data transmission for each terminal does not interfere with the data transmissions for other terminals.
A multiple-access system typically has many cells, where the term “cell” can refer to a base station and/or its coverage area depending on the context in which the term is used. Data transmissions for terminals in the same cell may be sent using orthogonal multiplexing to avoid “intra-cell” interference. However, data transmissions for terminals in different cells may not be orthogonalized, in which case each terminal would observe “inter-cell” interference from other cells. The inter-cell interference may significantly degrade performance for certain disadvantaged terminals observing high levels of interference.
To combat inter-cell interference, a wireless system may employ a frequency reuse scheme whereby not all frequency bands available in the system are used in each cell. For example, a system may employ a 7-cell reuse pattern and a reuse factor of K=7. For this system, the overall system bandwidth W is divided into seven equal frequency bands, and each cell in a 7-cell cluster is assigned one of the seven frequency bands. Each cell uses only one frequency band, and every seventh cell reuses the same frequency band. With this frequency reuse scheme, the same frequency band is only reused in cells that are not adjacent to each other, and the inter-cell interference observed in each cell is reduced relative to the case in which all cells use the same frequency band. However, a large reuse factor represents inefficient use of the available system resources since each cell is able to use only a fraction of the overall system bandwidth. More precisely, each cell is able to use only a reciprocal of the reuse factor, i.e., 1/K.
Active set based restricted frequency hopping (ASBR) reduces inter-cell interference in an OFDMA based system. ASBR is a global frequency planning scheme that takes into account the channel and interference measured by users. The key idea behind ASBR is to intelligently deploy frequency reuse for selected users based on their channel qualities. In CDMA systems, active set has been defined for each user for handoff purposes. Sectors in the active set of a user usually contribute most interference to this user's reception on FL and being interfered most severely by this user's transmission on RL. Avoiding interference from sectors in a user's active set is expected to reduce the interference on both FL and RL. Simulations and analysis have shown that the frequency reuse assignment algorithm based on a user's active set yields a 3.5 dB signal-to-interference and noise ratio (SINR) improvement with 25% bandwidth partial loading.
There is therefore a need in the art for techniques to provide feedback to a base station from a terminal to reduce inter-cell interference in a more efficient manner.